Psoriasis is a chronic, non-infectious inflammatory skin disease characterized by well-demarcated plaques where the cells proliferate quicker than normal (hyperprofileration), leading to a very dry and red skin. The proliferation rate of cells in the epidermis is controlled by the combination of the growth fraction and cell cycle time. In normal skin, the number of cells produced is balanced by the number of cells leaving the epidermal proliferative pool. The time required for a cell to transit between the basal layer and the stratum corneum of the skin (basically from birth to death and getting loose from the skin) is about 4 weeks, while for psoriasis patients, this time is substantially shorter (about 4 days).
Phototherapy has proven an effective treatment of psoriasis. These include broad-band ultraviolet B (UVB) radiation and narrow band UVB, photochemotherapy with psoralen plus ultraviolet A (PUVA), and UV laser. UVB radiation in a wavelength range of 305 to 314 nm has been proven most effective for the treatment of psoriasis.
Devices with PL or TL discharge lamps are known for full body or partial body treatments with narrow band (312 nm) radiation or UVA radiation. These devices do not allow for a specific dose depending on the severity of the plaque itself. Hence, they also irradiate healthy skin. Irradiation of the healthy skin can have negative effects such as ageing or even cancer.
Also handheld applicators are known that emit a narrow beam of radiation, for example from an excimer laser having a wavelength of 308 nm. Such a device allows the medical practitioner to accurately apply the radiation to the affected areas. This can however be an arduous task as the patient's skin may have hundreds or even thousands of mutually isolated affected areas. Furthermore in order for the treatment to be effective it has to be repeated numerous times. Even if the medical practitioner carries out this task in a very concentrated way it can hardly be prevented that certain affected areas are overtreated or remain untreated.
US patent application 2008/0051773 describes an apparatus for treating a skin condition with electromagnetic radiation comprising a source of the electromagnetic radiation and an image-shaping device configured to receive the electromagnetic radiation from the source. The apparatus further comprises a control system configured to cause the image-shaping device to form a shaped treatment image comprising the electromagnetic radiation on a patient's skin based on an image of the skin condition. FIG. 1 of the US patent application shows a camera 102 that captures images of an area 116 of the patient's skin. The control system (a computer 106) identifies psoriatic plaques 120 or other skin conditions to treat, and generates and transmits an appropriate treatment image to the projecting system 104. Ultraviolet light 122 from a laser 108 is focused by the optical system 110 onto an image-shaping device 112. The image-shaping device 112 generates the image from the computer 106 and imparts that image into the light 112 as it reflects it onto the patient's skin 118, through the focusing lens 114, to form a treatment image 124. The camera has a sufficient refresh rate to allow the treatment image to be updated quickly enough to compensate for a patient movement, such as breathing. In some examples the system is fully automated, capable of moving an arm 404 that positions the imaging head 406 to different areas of the patient's body as required.